A subsea wellhead assembly has separable tree modules that interconnect together. The lower tree module has a lower tree member having a bore with a valve for controlling production fluid flow. The upper tree module has an upper tree member with a bore and interface devices for monitoring the fluid flow as well as controlling the flow. A production line sub is carried alongside the upper tree member. The sub has a stab interface that stabs sealingly into a stab interface mounted alongside the lower tree member.